At least 3,500 people have been killed in Syria since major protests first broke out across the country in March, the UN said, as activists reported the deployment by security forces of tanks and armoured vehicles in the city of Hama.
Ravina Shamdasani, a spokeswoman for the UN High Commissioner for Human Rights, told reporters on Tuesday in Geneva that the estimate - which took the toll from 3,000 to 3,500 - was conservative and based on "credible sources on the ground".
She described the situation in Homs' neighbourhood of Baba Amro as "appalling", with residents deprived of food, water and medical supplies for a week. Activists reported that six people were killed in the central city, including one child.
President Bashar al-Assad's government has been battling protesters who are calling for his resignation in a crackdown that has seen some soldiers defecting and taking sides with the demonstrators.
The fighting in Homs, Syria's third-largest city, which entered its sixth day on Tuesday, has left more than 110 people dead, according to anti-government activists with the Local Co-ordination Committees (LCC).
The UN provided a lower estimated death toll, saying "more than 60" people had died in the city since the November 2 announcement of an Arab League ceasefire plan which appears to have had no effect in halting the government's crackdown.
Meanwhile, in Hama, around 50km north of Homs, tanks and armoured vehicles could be seen moving towards the city centre as snipers and armed government supporters surrounded a medical complex and the headquarters of the ruling Baath Party, the LCC said.
The activist network reported that five people were killed in Hama. Explosions and heavy gunfire could be heard in the city, and electricity and internet services had been disabled, they said.
|A resident of Hama tells Al Jazeera the city is living in fear amid a security crackdown.
Elsewhere in Syria, the LCC reported that seven people were killed in the northwestern provience in Idlib.
The opposition Syrian National Council, based in Turkey, urged the Arab League "to take a strong and effective position against the Syrian regime commensurate with the dangerous development of the situation in Syria, especially in ... Homs."
In a letter, it asked the pan-Arab bloc on Tuesday to freeze Syria's membership, impose economic and diplomatic sanctions, and seek the referral of allegations of genocide and other human rights abuses by the regime to the International Criminal Court.
The council, which represents the main opposition groups, focused its appeal on Homs, after declaring it a "humanitarian disaster area" in need of "international protection of civilians".
In recent weeks, violence between government forces and armed opposition groups in Homs appears to have risen, with defectors from the military using force to combat the regime.
A video posted on YouTube on Monday shows armed men in camouflage uniforms marching in Homs and proclaiming themselves defectors to the "Syrian Free Army".
In the video, one fighter calls for a no-fly zone and says that the uprising against Assad is peaceful.
'Lack of commitment'
The Arab League is expected to hold an emergency meeting on Saturday, which it says has been prompted by "the continuation of violence and because the Syrian government did not implement its commitments in the Arab plan to resolve the Syrian crisis".
In-depth coverage of escalating violence across Syria
Sheikh Hamad bin Jassim Al Thani, the Qatari prime minister and chair of a panel on the crisis, has said that "if Syria does not respect its commitments, the ministerial committee will meet again and take the necessary decisions".
The Arab roadmap called for an end to violence, the release of those detained, the withdrawal of the army from urban areas and free movement for observers and the media, as well as talks between the regime and the opposition.
Despite the deaths, a large section of the population, including businesspeople and minorities, seems to be still loyal to the government of Assad, who has been in power for 11 years.
Large pro-government demonstrations can be seen regularly, and major cities such as Damascus and Aleppo have so far not become protest hubs like Hama, Homs and Deraa.